A strong rise in non-regular employment has posed a major challenge to Japanese trade unions which have long limited membership to regular employees. However, a number of mainstream unions in the retail industry have responded by organizing non-regular workers. The article draws on a series of semi-structured interviews with union representatives to analyse the initiatives by the industrial federation UA Zensen and three affiliated enterprise unions. It addresses the implications for both the workers and the unions concerned. Unions have provided a stronger voice to nonregular workers and negotiated better working conditions. However, it has not brought material equality with regular workers or major changes to Japanese unionism. Instead, the enterprise-based and cooperative nature of unionism has shaped the initiatives and reproduced traditional equilibria and processes between labour and management, thus constraining the ability of unions to develop a strong stance for the emancipation of non-regular workers.